BMR Calculator: What Your Body Burns Doing Nothing
This BMR calculator estimates the energy you would spend lying perfectly still for 24 hours — and then shows what that figure becomes once an ordinary day is layered on top of it.
Mifflin-St Jeor equation. This is energy at complete rest, not a food target.
Estimated daily burn at each activity level
- SedentaryDesk job, little or no exercise —kcal
- Lightly activeLight exercise 1–3 days/week —kcal
- Moderately activeExercise 3–5 days/week —kcal
- ActiveHard exercise 6–7 days/week —kcal
- Very activeHard daily training or a physical job —kcal
All five are shown on purpose: your real day sits somewhere in this range, and no single row is the “right” one.
What this BMR calculator does
Your basal metabolic rate is the energy bill for staying alive: heartbeat, breathing, kidney filtration, immune activity, the constant rebuilding of cells. It runs whether you are asleep, reading, or stuck in traffic, and for most adults it accounts for somewhere between 60% and 70% of everything they burn in a day.
People look for this tool under a dozen names — a calculator for basal metabolic rate, a calculator for metabolic rate, even a basal metabolic weight calculator — and the arithmetic behind every one of them is the same. Spelling rarely matters either: whether you searched for bmr compute, bmr computation, or the frequent typo calculare bmr, you have landed on the page that answers it.
If you were trying to find bmr calculator results without installing anything, this bmr online calculator runs entirely inside your browser. Nothing is uploaded, nothing is stored, and it behaves as the same online metabolic rate calculator on a phone as it does on a laptop.
The basal metabolic rate formula
This page uses Mifflin-St Jeor, published in 1990 and still the default in clinical practice because it was fitted on a large, ordinary adult sample rather than a small athletic one:
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
Read it left to right and the logic is plain. Mass costs the most, which is why weight carries the biggest coefficient. Height adds surface area to keep warm. Age subtracts, because resting expenditure drifts down over the decades as lean tissue is slowly lost. The final constant is what separates the two versions of the basal metabolic rate formula.
Worked example. A 30-year-old woman, 165 cm and 62 kg: 620 + 1,031 − 150 − 161 ≈ 1,340 kcal a day at rest.
What BMR is not
On its own, a resting figure is close to useless for planning — nobody spends the day motionless. That is why the result above is followed immediately by five numbers rather than one. Multiply BMR by an activity factor and you get total daily energy expenditure: what you actually burn.
| Level | Multiplier | A typical week |
|---|---|---|
| Sedentary | 1.20 | Desk-based, little or no structured exercise. |
| Lightly active | 1.375 | Light exercise or sport one to three days. |
| Moderately active | 1.55 | Moderate exercise three to five days. |
| Active | 1.725 | Hard exercise six to seven days. |
| Very active | 1.90 | Hard daily training plus physical work. |
Most people place themselves a rung too high, so when two rows both sound plausible, take the lower one. If you want the same calculation with a choice of equations and a visual split between resting and activity energy, the TDEE calculator has it.
BMR, RMR and TDEE: three numbers, one family
- BMR — measured under strict conditions: fully rested, fasted, lying down, in a thermally neutral room.
- RMR — resting metabolic rate, the same idea with the strict conditions relaxed. It comes out roughly 5–10% higher and the two terms are often used interchangeably.
- TDEE — everything together: resting energy, digestion, fidgeting, walking, training.
Prediction equations technically estimate something closer to RMR than to true laboratory BMR. The gap is small next to the error introduced by guessing your activity level, so it rarely changes a decision.
What moves your basal rate
Body size dominates: a taller, heavier person has more tissue to keep running and burns more at rest, full stop. Lean mass matters within that, because muscle, organs and brain are metabolically busy while stored fat is comparatively quiet. Age nudges it down slowly. Sex appears in the equation largely as a stand-in for average differences in body composition. Thyroid function, illness, fever and pregnancy can all shift it, sometimes substantially.
What deserves saying plainly: a number here is not a verdict. A high resting rate is not fitness, and a low one is not a personal failing — mostly it reflects how much of you there is. If you know your body fat percentage, the Katch-McArdle option in the TDEE tool works from lean mass instead and often suits very lean or very muscular people better.
Frequently Asked Questions
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Four numbers are enough to determine BMR: sex, age, height and weight. Feed them into the Mifflin-St Jeor equation and you determine basal metabolic rate in kcal per day. Nothing else is required to determine metabolic rate at rest — no lab, no wearable, no body-composition scan.
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You can figure out BMR with a pen: multiply your weight in kilograms by 10, add 6.25 times your height in centimetres, subtract 5 times your age, then add 5 if you are male or subtract 161 if you are female. That arithmetic is all it takes to figure out basal metabolic rate, and the same three terms figure out metabolic rate for anyone.
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The basal metabolic rate formula used here is Mifflin-St Jeor (1990): BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age, then +5 for men and −161 for women. It was fitted on a large adult sample and is the equation most dietitians reach for first.
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Yes. A lab measures resting energy use through indirect calorimetry, breath by breath. An equation cannot match that, but it will estimate basal metabolic rate to within roughly 10% for most adults of average build, which is close enough for planning food and training.
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Neither. BMR mostly tracks how much body you have to run: taller, heavier and more muscular people burn more at rest simply because there is more tissue to maintain. A high figure is not fitness and a low one is not a fault — it is a scale reading, not a score.
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Prediction equations land within about 10% of measured resting metabolism for most people, and drift further at the extremes of height, weight and body composition. Use the number as a starting point and let real-world results — weight trend over two to three weeks — correct it.